These kinds of experiences mean nothing; they are purely anecdotal. They are just small samples that are statistically meaningless. As others have mentioned, what about all the non-JWs who perform good deeds? I currently work for a small business and on jobs we do, there are all kinds of different materials and labor involved. There can be ten or more different items that we internally itemize for jobs (the customer only sees the overall price). Even though it would be easy to overcharge a little, the owners are completely honest and fair with customers and subcontractors. They are not JWs, so what does that mean?
On the other hand, I know a number of JWs who have been dishonest and have been outright thieves. For example, one worked for a major delivery company and was caught stealing major items that he was supposed to be delivering - like laptop computers. An older female worked for a doctor's office and was caught stealing prescription drugs. An older ministerial servant, was caught stealing money from his congregation (from the literature department back when money was collected for literature). So, what does that mean?